Medical instruments and devices typically are provided to a practitioner in a sterile condition. This particularly is true of such instruments that are utilized for providing a desired medicament, imaging agent or other liquid for parenteral administration, such as a hypodermic syringe or the like.
A syringe typically includes some type of barrel, vial or cartridge having a desired medicament, imaging agent or other liquid therein for parenteral administration and is manufactured sterile primarily by two methods. The first method utilizes aseptic techniques and includes, for example, individually sterilizing the elements of the syringe, assembling the elements, filling the syringe with a desired medicament in an aseptic environment and packaging the assembled syringe for later use. This method, however, is susceptible to contamination during the assembly and packaging of the device.
A second method is referred to as "terminal sterilization" where the completely assembled syringe filled with medicament is sterilized, typically by steam, and then packaged for later use. Such a method or process ensures that the medicament, imaging agent or other contents of the syringe, as well as the individual syringe elements, are provided in a sterile condition at the point of use.
Terminally sterilizing a prefilled device containing a desired medicament, such as a syringe, typically is accomplished with steam in an autoclave. The heat and pressure generated in the autoclave, however, can have an adverse effect on the device.
For example, vapor pressure and thermal expansion of the medicament in the syringe can cause the syringe sealing members, such as a stopper or end cap, to blow out. Additionally, if the barrel or other elements of the syringe are formed from plastic, the heat and pressure generated by the autoclave can deform these members and inhibit their performance during use.
An example of an existing method for terminally sterilizing prefilled syringes is illustrated in U.S. Pat. No. 4,718,463. That patent substantially discloses washing the barrel of the syringe with repeated water jet washings, preferably ten washings, filling the barrel through its open end, assembling the piston in the open end, sealing the syringe and its contents and then autoclaving the assembled and sealed syringe. During autoclaving, the pressure on the outside surfaces of the syringe is maintained at least equal to the pressure of the syringe contents and the syringe is preferably heated to a temperature between 120.degree. and 125.degree. C.
With this method, however, filling the syringe and inserting the plunger or piston through the open end of the syringe barrel requires complex filling and sealing equipment. Additionally, when filling and sealing from the open end of the syringe barrel, a selected amount of inert gas is included within the barrel which is not acceptable in many applications. Also, sterilizing between 120.degree. and 125.degree. C. limits syringe barrel material choices, particularly material which would have improved clarity.
Another example of an existing method for terminally sterilizing prefilled syringes is illustrated in U.S. Pat. No. 5,207,983. That patent substantially discloses steam sterilizing of a syringe by autoclaving where 2-10% empty space is provided between the plunger and the distal or closed end of the syringe barrel and at least 10% empty space is provided between the plunger and the proximal or open end of the syringe barrel. The 10% empty space allows for sliding movement of the plunger toward the proximal end of the barrel in response to internal pressure generated during autoclaving and preferably requires at least one temperature/pressure measuring device in direct contact with the contents of at least one sample syringe for monitoring and regulating temperature and pressure within the autoclave.
With this method, however, no initial cleaning or steam sterilization prior to terminal sterilization is required, but a more complicated autoclaving process is utilized. Initial cleaning removes any particulates which may be present within the syringe barrel or other elements which may cause contamination while steam sterilization insures microbial "kill" and maintains a necessary degree of moisture within the syringe elements, particularly the stopper or plunger.
Furthermore, this method would appear to provide less medicament with the same size syringe due to the requirement of at least 10% empty space within the syringe to allow for plunger expansion. Although a larger syringe can be utilized to provide the same measured amount of medicament which is customary in the medical field, a larger syringe could be confusing to a practitioner and may require different packaging. Additionally, if the proper plunger expansion room is not provided or the preferred conditions within the autoclave are not maintained, the plunger will blow out of the syringe.
It therefore would be desirable to provide a process or method for prefilling and terminally sterilizing syringes which substantially eliminates air within the syringe barrel, does not require expansion space for the stopper and terminally sterilizes the filled syringe without deforming the syringe or causing the stopper or plunger to blow out. Such a process not only ensures a sterilized filled syringe but eliminates air from the syringe barrel that could cause plunger blow out or be ejected out of the syringe by a practitioner.